From: terje.mathisen@tmsw.no   
      
   Michael S wrote:   
   > On Tue, 6 Jan 2026 12:35:20 +0100   
   > Terje Mathisen  wrote:   
   >   
   >> Thomas Koenig wrote:   
   >>> Michael S  schrieb:   
   >>>> On Sun, 4 Jan 2026 00:21:31 -0000 (UTC)   
   >>>> Thomas Koenig  wrote:   
   >>>>   
   >>>>>   
   >>>>> And two decimal flavors, as well, with binary and densely packed   
   >>>>> decimal encoding of the significand... it's a bit of a mess.   
   >>>>>   
   >>>>   
   >>>> Since both formats have exactly identical semantics, in theory the   
   >>>> mess is not worse (and not better) than two bytes orders of IEEE   
   >>>> binary FP.   
   >>>   
   >>> Almost.   
   >>>   
   >>> IIRC, there is no restriction on the binary mantissa, so its   
   >>> range is slightly larger for the same number of bits   
   >>> (1000/1024)**(n/3).   
   >>>   
   >> Sorry, that's wrong:   
   >>   
   >> Just like the 24 "spare" DPD patterns are illegal,   
   >   
   > Non-canonical, which is not the same as illegal   
   > Silently accepted as input operands but never produced as result.   
   >   
   >> any mantissa   
   >> corresponding to a number greater than the maximum allowed (1e34   
   >> afair) is also illegal, and there are rules for how to handle both   
   >> cases (without checking, i seem to remember that they should be   
   >> treated as zero?)   
   >>   
   >   
   > BID significand extension > max is indeed treated as zeros.   
   > Non-canonical DPD declets have non-zero values.   
   > They are forms of (8+c)*100 + (8+f)*10 + (8+i), where c, f, and i are   
   > in range [0:1].   
      
   OK, that is probably because allowing them on input is significantly   
   faster/cheaper than having to detect and modify/trap/erase.   
      
   That said, out of range mantissas could also have been accepted, except   
   they would not have had a valid conversion to either DPD or ascii.   
      
   Terje   
      
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